EESPONSE AND IN THE LIVING NON-LIVING RESPONSE IN THE LIVING AND NON-LIVING BY JAGADIS CHUNDER BOSE, M. A. (CANTAB.), D.Sc.(LoND.) PROFESSOK, PRESIDENCY COLLEGE, CALCUTTA WITH ILLUSTRATIONS LONGMANS, GEEEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK AND BOMBAY 1902 All rights reserved The real is one : wise men call it variously ' RIG VEDA To my Countrymen This Work is Dedicated PKEFACE I HAVE in the present work put in a connected and a more complete form results, some of which have been published in the following Papers : ' De la Generality des Phenomenes Moleculaires produits par 1'Electricite sur la matiere Inorganique et sur la matiere Vivante.' (Travaux du Congres International de Physique. Paris, 1900.) ' On the Similarity of Effect of Electrical Stimulus on Inorganic and Living Substances.' (Report, Bradford Meeting British Association, 1900. — Electrician.) 'Kesponse of Inorganic Matter to Stimulus.' (Friday Evening Discourse, Koyal Institution, May 1901.) 4 On Electric Eesponse of Inorganic Substances. Preliminary Notice.' (Koyal Society, June 1901.) ' On Electric Eesponse of Ordinary Plants under Me- chanical Stimulus.' (Journal Linnean Society, 1902.) 1 Sur la Reporise Electrique dans les Metaux, les Tissus A19n0i2.m)aux et Vegetaux.' (Societe de Physique, Paris, ' On the Electro-Motive Wave accompanying Mechanical Disturbance in Metals in contact with Electrolyte.' (Proceedings Royal Society, vol. 70.) * On the Strain Theory of Vision and of Photographic Action.' (Journal Royal Photographic Society, vol. xxvi.) viii RESPONSE IN THE LIVING AND NON-LIVING These investigations were commenced in India, and I take this opportunity to express my grateful acknowledgments to the Managers of the Eoyal Institution, for the facilities offered me to complete them at the Davy-Faraday Laboratory. J. C. BOSE. DAVY-FARADAY LABORATORY, ROYAL INSTITUTION, LONDON: May 1902. CONTENTS CHAPTEE I THE MECHANICAL RESPONSE OF LIVING SUBSTANCES PAGE Mechanical response — Different kinds of stimuli — Myograph — Charac- teristics ofresponse-curve : period, amplitude, form — Modification of response-curves ......... 1 CHAPTEE II ELECTEIC RESPONSE Conditions for obtaining electric response — Method of injury — Current of injury — Injured end, cuproid : uninjured, zincoid — Current of response in nerve from more excited to less excited — Difficulties of present nomenclature — Electric recorder — Two types of response, positive, and negative — Universal applicability of electric mode of response — Electric response a measure of physiological activity — Electric response in plants CHAPTEE III ELECTRIC RESPONSE IN PLANTS — METHOD OF NEGATIVE VARIATION Negative variation — Response recorder — Photographic recorder — Compensator — Means of graduating intensity of stimulus — Springtapper and torsional vibrator — Intensity of stimulus dependent on amplitude of vibration— Effectiveness of stimulus dependent on rapidity also . 17 RESPONSE IN THE LIVING AND NON-LIVING CHAPTEK IV ELECTRIC RESPONSE IN PLANTS — BLOCK METHOD PAGE Method of block— Advantages of block method— Plant response a physiological phenomenon — Abolition of response by anaesthetics and poisons — Abolition of response when plant is killed by hot water . 27 CHAPTEE V PLANT RESPONSE — ON THE EFFECTS OF SINGLE STIMULUS AND OF SUPERPOSED STIMULI Effect of single stimulus — Superposition of stimuli — Additive effect — Staircase effect— Fatigue — No fatigue when sufficient interval between stimuli — Apparent fatigue when stimulation frequency is increased — Fatigue under continuous stimulation ... 35 CHAPTEE VI PLANT RESPONSE— ON DIPHASIC VARIATION Diphasic E.M. variation— variation Positive after-effect and positive response— ...... Eadial 44 CHAPTEE VII PLANT RESPONSE — ON THE RELATION BETWEEN STIMULUS AND RESPONSE Increased response tion ofresponse with increasing stimulus— Apparent diminuwith excessively strong stimulus .... 51 CONTENTS xi CHAPTEE VIII PLANT RESPONSE — ON THE INFLUENCE OF TEMPERATURE PAGE Effect of very low temperature — Influence of high temperature — Determination of death-point —Increased response as after-effect of temperature variation — Death of plant and abolition of response bv the action of steam . 59 CHAPTEK IX PLANT RESPONSE — EFFECT OF ANESTHETICS AND POISONS Effect of anaesthetics, a test of vital character of response — Effect of chloroform — Effect of chloral — Effect of formalin — Method in which response is unaffected by variation of resistance — Advantage of block method— Effect of dose . 7 1 CHAPTEE X RESPONSE IN METALS Is response found in inorganic substances? — Experiment on tin, block method — Anomalies of existing terminology — Response by method of depression — Response by method of exaltation .... 81 CHAPTEE XI INORGANIC RESPONSE — MODIFIED APPARATUS TO EXHIBIT RESPONSE IN METALS Conditions of obtaining quantitative measurements — Modification of the block method — Vibration cell — Application of stimulus — Graduation of the intensity of stimulus — Considerations showing that electric response is due to molecular disturbance — Test experi- ment— Molecular voltaic cell .... 91 xii RESPONSE IN THE LIVING AND NON-LIVING CHAPTER XII INORGANIC RESPONSE— METHOD OF ENSURING CONSISTENT RESULTS PAGE Preparation of wire— Effect of single stimulus 100 - CHAPTER XIII INORGANIC RESPONSE — MOLECULAR MOBILITY I ITS INFLUENCE ON RESPONSE Effects of molecular inertia — Prolongation of period of recovery by overstrain — Molecular model — Reduction of molecular sluggishness attended by quickened recovery and heightened response — Effect of temperature — Modification of latent period and period of recovery by the action of chemical reagents — Diphasic variation . 104 CHAPTER XIV INORGANIC RESPONSE— FATIGUE, STAIRCASE, AND MODIFIED RESPONSE Fatigue in metals —Fatigue under continuous stimulation — Staircase effect — Reversed responses due to molecular modification in nerve and in metal, and their transformation into normal after continuous stimulation — Increased response after continuous stimulation . 118 CHAPTER XV INORGANIC RESPONSE — RELATION BETWEEN STIMULUS AND RESPONSE — SUPERPOSITION OF STIMULI Relation between stimulus and response — Magnetic analogue — In- crease ofresponse with increasing stimulus — Threshold of response — Superposition of stimuli — Hysteresis 131 CONTENTS xiii CHAPTEE XVI INORGANIC RESPONSE — EFFECT OF CHEMICAL REAGENTS PAGE Action of chemical reagents — Action of stimulants on metals — Action of depressants on metals — Effect of ' poisons ' on metals — Opposite effect of large and small doses 139 CHAPTEE XVII ON THE STIMULUS OF LIGHT AND RETINAL CURRENTS Visual impulse : (1) chemical theory ; (2) electrical theory — Retinal currents — Normal response positive — Inorganic response under stimulus of light — Typical experiment on the electrical effect in- duced bylight .......... 148 CHAPTEE XVIII INORGANIC RESPONSE — INFLUENCE OF VARIOUS CONDITIONS ON THE RESPONSE TO STIMULUS OF LIGHT Effect of temperature — Effect of increasing length of exposure — Relation between intensity of light and magnitude of response — After- oscillation — Abnormal effects: (1) preliminary negative twitch ; (2) reversal of response ; (3) transient positive twitch on cessation of light ; (4) decline and reversal — Resume ..... 158 CHAPTEE XIX VISUAL ANALOGUES Effect of light of short duration — After-oscillation — Positive and nega- tive after-images — Binocular alternation of vision — Period of alter- nation modified by physical condition — After-images and their revival — Unconscious visual impression ..... 170 CHAPTEE XX GENERAL SURVEY AND CONCLUSION . . 181 INDEX 193 ILLUSTKATIONS FIG. 1*AGE 1. MECHANICAL LEVER RECORDER 3 2. ELECTKIC METHOD or DETECTING NERVE RESPONSE .. 6 3. DIAGRAM SHOWING INJURED END OF NERVE CORRESPONDS TO COPPER IN A VOLTAIC ELEMENT 8 4. ELECTRIC RECORDER 11 5. SIMULTANEOUS RECORD OF MECHANICAL AND ELECTRICAL RESPONSES 13 6. NEGATIVE VARIATION IN PLANTS 19 7. PHOTOGRAPHIC RECORD OF NEGATIVE VARIATION IN PLANTS 20 8. RESPONSE RECORDER 21 ». THE COMPENSATOR 22 10. THE SPRING-TAPPER 23 11. THE TORSIONAL VIBRATOR 24 12. RESPONSE IN PLANT TO MECHANICAL TAP OR VIBRATION . 25 13. INFLUENCE OF SUDDENNESS ON THE EFFICIENCY OF STIMULUS 26 14. THE METHOD OF BLOCK 28 15. RESPONSE IN PLANT COMPLETELY IMMERSED UNDER WATER 29 16. UNIFORM RESPONSES IN PLANT . . . . . . 36 17. FUSION OF EFFECT UNDER RAPIDLY SUCCEEDING STIMULI IN MUSCLE AND IN PLANT 36 18. ADDITIVE EFFECT OF SINGLY INEFFECTIVE STIMULI ON PLANT 37 19. 'STAIRCASE EFFECT' IN PLANT 37 20. APPEARANCE OF FATIGUE IN PLANT UNDER SHORTENED PERIOD OF REST 39 xvi RESPONSE IN THE LIVING AND NON-LIVING F 21. FATIGUI E IN CG EL. ERY I>A<;K . 40 22. FATIGUE IN CAULIFLOWER-STALK 23. FATIGUE FROM PREVIOUS OVERSTRAIN . . . 41 41 24. FATIGUE UNDER CONTINUOUS STIMULATION IN CELERY . . 42 25 EFFECT OF REST IN REMOVAL OF FATIGUE IN PLANT . . 43 26. DIPHASIC VARIATION IN PLANT . ... 46 27,28. ABNORMAL POSITIVE RESPONSES IN STALE PLANT TRANS- FORMED INTO NORMAL NEGATIVE UNDER STRONG STIMU- LATION . 48, 49 29. RADIAL E.M. VARIATION . . . 50 30. CURVES SHOWING THE RELATION BETWEEN INTENSITY OF STIMULUS AND RESPONSE IN MUSCLE AND NERVE . . 52 31. INCREASING RESPONSES TO INCREASING STIMULI (TAPS) IN PLANTS 52 32. INCREASING RESPONSES TO INCREASING VJBRATIONAL STIMULI IN PLANTS 53 33. RESPONSES TO INCREASING STIMULI IN FRESH AND STALE SPECIMENS OF PLANTS ........ 54 34. APPARENT DIMINUTION OF RESPONSE CAUSED BY FATIGUE UNDER STRONG STIMULATION 57 35. DIMINUTION OF RESPONSE IN EUCHARIS LILY AT Low TEM- PERATURE 61 36. RECORDS SHOWING THE DIFFERENCE IN THE EFFECTS OF Low TEMPERATURE ON IVY, HOLLY, AND EUCHARIS LILY . 62 37. PLANT CHAMBER FOR STUDYING THE EFFECT OF TEMPERA- TURE AND ANESTHETICS 64 38. EFFECT OF HIGH TEMPERATURE ON PLANT RESPONSE . . 64 39. AFTER-EFFECT ON THE RESPONSE DUE TO TEMPERATURE VARIATION . . . 66 40. RECORDS OF RESPONSES IN EUCHARIS LILY DURING RISE AND FALL OF TEMPERATURE 67 41. CURVE SHOWING VARIATION OF SENSITIVENESS DURING A CYCLE OF TEMPERATURE VARIATION . . . . . 68 42. RECORD OF EFFECT OF STEAM IN ABOLITION OF RESPONSE AT DEATH OF PLANT . AQ ILLUSTRATIONS xvii Fit!. 43. EFFECT OF CHLOROFORM ON NEKVE RESPONSE . . 44. EFFECT OF CHLOROFORM ON THE RESPONSES OF CARROT PAGE . . 72 . 74 45. ACTION OF CHLORAL HYDRATE ON PLANT RESPONSES 46. ACTION OF FORMALIN ON RADISH . . 75 75 47. ACTION OF SODIUM HYDRATE IN ABOLISHING THE RESPONSE IN PLANT 78 48. STIMULATING ACTION OF POISON IN SMALL DOSES IN PLANTS 79 49. THE POISONOUS EFFECT OF STRONGER DOSE OF KOH . . 79 50. BLOCK METHOD FOR OBTAINING RESPONSE IN TIN . . . 83 51. RESPONSE TO MECHANICAL STIMULATION IN A ZN-Cu COUPLE 85 52. ELECTRIC RESPONSE IN METAL BY THE METHOD OF RELATIVE DEPRESSION (NEGATIVE VARIATION) . . . .88 53. METHOD OF RELATIVE EXALTATION 89 54. VARIOUS CASES OF POSITIVE AND NEGATIVE VARIATION . 90 55. MODIFICATIONS OF THE BLOCK METHOD FOR EXHIBITING ELECTRIC RESPONSE IN METALS 93 56. EQUAL AND OPPOSITE RESPONSES GIVEN BY Two ENDS OF THE WIRE 95 57. TOP VIEW OF THE VIBRATION CELL 96 58. INFLUENCE OF ANNEA ING IN THE ENHANCEMENT OF RESPONSE IN METALS 101 59. UNIFORM ELECTRIC RESPONSES IN METALS . . . . 102 60. PERSISTENCE OF AFTER-EFFECT 105 61. PROLONGATION OF PERIOD OF RECOVERY AFTER OVERSTRAIN 106 62. MOLECULAR MODEL 107 63. 64. EFFECTS OF REMOVAL OF MOLECULAR SLUGGISHNESS IN QUICKENED RECOVERY AND HEIGHTENED RESPONSE IN METALS 109,110 65. EFFECT OF TEMPERATURE ON RESPONSE IN METALS. . . Ill 66. DIPHASIC VARIATION IN METALS 113 67. NEGATIVE, DIPHASIC, AND POSITIVE RESULTANT RESPONSE IN METALS . 115 xviii RESPONSE IN THE LIVING AND NON-LIVING PACK 68. CONTINUOUS TRANSFORMATION FROM NEGATIVE TO POSITIVE THROUGH INTERMEDIATE DIPHASIC KESPONSE . .116 69. FATIGUE IN MUSCLE .... ... 118 70. FATIGUE IN PLATINUM .... .118 71. FATIGUE IN TIN. .... . . 119 72. APPEARANCE OF FATIGUE DUE TO SHORTENING THE PERIOD OF RECOVERY 120 73. FATIGUE IN METAL UNDER CONTINUOUS STIMULATION . . 121 74. 'STAIRCASE' RESPONSE IN MUSCLE AND IN METAL . .122 75. ABNORMAL RESPONSE IN NERVE CONVERTED INTO NORMAL UNDER CONTINUED STIMULATION 124 76. 77. ABNORMAL RESPONSE IN TIN AND PLATINUM CONVERTED INTO NORMAL UNDER CONTINUED STIMULATION . . 125 78. GRADUAL TRANSITION FROM ABNORMAL TO NORMAL RESPONSE IN PLATINUM 126 79. INCREASE OF RESPONSE IN NERVE AFTER CONTINUOUS STIMULATION 127 80, 81. RESPONSE IN TIN AND PLATINUM CONTINUOUS STIMULATION 82. MAGNETIC ANALOGUE ENHANCED AFTER 127, 128 132 83,84. RECORDS OF RESPONSES TO INCREASING STIMULI IN TIN 134, 135 85. INEFFECTIVE STIMULUS BECOMING EFFECTIVE BY SUPER- POSITION 135 86. INCOMPLETE AND COMPLETE FUSION OF EFFECTS . . . 136 87. CYCLIC CURVE FOR MAXIMUM EFFECTS SHOWING HYSTERESIS 137 88. ACTION OF POISON IN ABOLISHING RESPONSE IN NERVE . . 139 89. ACTION OF STIMULANT ON TIN 141 90. ACTION OF STIMULANT ON PLATINUM 142 91. DEPRESSING EFFECT OF KBn ON TIN 143 92. ABOLITION OF RESPONSE IN METALS BY < POISON ' . . . 143 03. « MOLECULAR ARREST ' BY THE ACTION OF < POISON ' . .145 94. OPPOSITE EFFECTS OF SMALL AND LARGE DOSES ON THE RESPONSE IN METALS . 146 95. RETINAL RESPONSE TO LIGHT 150 ILLUSTRATIONS xix FIG. PAGE 96. RESPONSE OF SENSITIVE CELL TO LIGHT 152 97. TYPICAL EXPERIMENT ON THE E.M. VARIATION PRODUCED BY LIGHT 154 98. MODIFICATION OF THE PH•OTO-SENSITIVE CELL . . . . 155 99. RESPONSES IN FROG'S RETINA 156 100. RESPONSES IN SENSITIVE PHOTO-CELL 157 101. EFFECT OF TEMPERATURE ON THE RESPONSE TO LIGHT STIMULUS 159 102. EFFECT OF DURATION OF EXPOSURE ON THE RESPONSE . . 159 103. RESPONSES OF SENSITIVE CELL TO INCREASING INTENSITIES OF LIGHT 161 104. RELATION BETWEEN THE INTENSITY OF LIGHT AND MAGNI- TUDE OF RESPONSE 162 105. AFTER-OSCILLATION 163 106. TRANSIENT POSITIVE INCREASE OF RESPONSE IN THE FROG'S RETINA ON THE CESSATION OF LIGHT 164 107. TRANSIENT POSITIVE INCREASE SENSITIVE CELL OF RESPONSE IN THE 165 108. DECLINE UNDER THE CONTINUOUS ACTION OF LIGHT . . 166 109. CERTAIN AFTER-EFFECTS OF LIGHT 168 110. AFTER-EFFECT OF LIGHT OF SHORT DURATION . . . . 172 111. STEREOSCOPIC DESIGN FOR THE EXHIBITION OF BINOCULAR ALTERNATION OF VISION 176 112. UNIFORM RESPONSES IN NERVE, PLANT, AND METAL . . 184 113. FATIGUE IN MUSCLE, PLANT, AND METAL .... 185 114. 'STAIRCASE' EFFECT IN MUSCLE, PLANT, AND METAL . . 186 115. INCREASE OF RESPONSE AFTER CONTINUOUS STIMULATION IN NERVE AND METAL . . . . . . .186 116. MODIFIED ABNORMAL RESPONSE IN NERVE AND METAL TRANSFORMED INTO NORMAL RESPONSE AFTER CONTINUOUS STIMULATION 187 117. ACTION OF THE SAME ' POISON' IN THE ABOLITION OF RE- SPONSE IN NERVE, PLANT, AND METAL .... 189 RESPONSE IN THE LIVING AND NON-LIVING OHAPTEE I THE MECHANICAL RESPONSE OF LIVING SUBSTANCES Mechanical response — Different kinds of stimuli — Myograph — Characteristics of response-curve : period, amplitude, form — Modification of response-curves. ONE of the most striking effects of external disturbance on certain types of living substance is a visible change of form. . Thus, a piece of muscle when pinched con- tracts. The external disturbance which, produced this change is called the stimulus. The body which is thus capable of responding is said to be irritable or excit- able.; Astimulus thus produces a state of excitability which may sometimes be expressed by. change of form. Mechanical response to different kinds of stimuli.— This reaction under stimulus is seen even in the lowest organisms ; in some of the amoeboid rhizopods, for instance. These lumpy protoplasmic bodies, usually elongated while creeping, if mechanically jarred, con- tract into a spherical form. If, instead of mechanical B 2 RESPONSE IN THE LIVING AND NON-LIVING disturbance, we apply salt solution, they again contract, in the same way as before. Similar effects are produced by sudden illumination, or by rise of temperature, or by electric shock. A living substance may thus be put into an excitatory state by either mechanical, chemical, thermal, electrical, or light stimulus. Not only does the point stimulated show the effect of stimulus, but that effect may sometimes be conducted even to a considerable distance. This power of conducting stimulus, though common to all living substances, is present in very different degrees. While in some forms of animal tissue irritation spreads, at a very slow rate, only to points in close neighbourhood, in other forms, as for example in nerves, conduction is very rapid and reaches far. The visible mode of response by change of form may perhaps be best studied in a piece of muscle. When this is pinched, or an electrical shock is sent through it, it becomes shorter and broader. A responsive twitch is thus produced. The excitatory state then disappears, and the muscle is seen to relax into its normal form. Mechanical lever recorder.— In the case of contrac- tion of muscle, the effect is very quick, the twitch takes place in too short a time for detailed observation by ordinary means. A myographic apparatus is therefore used, by means of which the changes in the muscle are self-recorded. Thus we obtain a history of its change and recovery from the change. The muscle is connected to one end of a writing lever. When the muscle contracts, the tracing point is pulled up in one THE MECHANICAL RESPONSE 3 direction, say to the right. The extent of this pull depends on the amount of contraction. A band of paper or a revolving drum-surface moves at a uniform speed at right angles to the direction of motion of the writing lever. When the muscle recovers from the stimulus, it relaxes into its original form, and the writing point traces the recovery as it moves now to the left, regaining its first position. A curve is thus described, the rising portion of which is due to contraction, and the falling portion to relaxation or recovery. The ordinate of the curve represents the intensity of response, and the abscissa the time , FIG. 1. — MECHANICAL LEVER . 1). BECORDER Cr*hhanrfacn/t*ef rAi«s-iteifciVso 0e\1f tf nVIeA rt- AeosnpromnosAe-Thebomnuesclies seMcuwrietihy thheeldattaatchoende (It)\ fP*»erriinOHd, ((2?)\ AAmtnpnlliitfuiidHe*,* neencdt,edthewioththetrhe end being conwriting lever. (3) Form.-Just as a wave of sound is characterised by its (1) period, (2) a. mplit- ude, , and (3) for, m, ,s. o these response-Curves be dlS- t„ rom ea" ch Other. AS regards_the peri. od, there is an scluerfreac.ovrearswhf?rnom contrac- tion,thetracingpointreturns oton itPs otrhieginraelcoprodsitioofn.muscSleee curve. enormous variation, corresponding to the functional activity of the muscle. For instance, in tortoise it may be as high as a second, whereas in the wing-muscles of many insects it is as small as -^^ part of a second. * It is probable that a continuous graduated scale might, as suggested by Hermann, be drawn up in the animal kingdom, from the excessively rapid contraction of B 2 4 RESPONSE IN THE LIVING AND NON-LIVING insects to those of tortoises and hibernating dormice.' * Differences in form^and amplitude of curve are well illustrated by various muscles of the tortoise. The curve for the muscle of the neck, used for rapid with- drawal of the head on approach of danger, is quite different from that of the pectoral muscle of the same animal, used for its sluggish movements. Again, progressive changes in the same muscle are well seen in the modifications of form which consecutive muscle-curves gradually undergo. In a dying muscle* for example, the amplitude of succeeding curves is con- tinuously diminished, and the curves themselves are elongated. Numerous illustrations will be seen later, of the effect, in changing the form of the curve, of the> increased excitation or depression produced by various agencies. Thus these response records give us a means of studying the effect of stimulus, and the modification of response, under varying external conditions, -advantage being taken of the mechanical contraction produced in the tissue by the stimulus. But there are other kinds of tissue where the excitation produced by stimulus is not exhibited in a visible form. In order to study these we have to use an altogether independent method, the method of electric response. 1 Biedermann, Electro-physiology, p. 59. CHAPTEE II ELECTRIC RESPONSE Conditions for obtaining electric response — Method of injury — Current of injury — Injured end, cuproid: uninjured, zincoid — Current of response in nerve from more excited to less excited — Difficulties of present nomenclature— Electric recorder — Two types of response, positive and negative — Universal applicability of electric mode of response — Electric response a measure of physiological activity — Electric response in plants. UNLIKE muscle, a length of nerve, when mechanically or electrically excited, does not undergo any visible change. That it is thrown into an excitatory state, and that it conducts the excitatory disturbance, is shown however by the contraction produced in an attached piece of muscle, which serves as an indicator. But the excitatory effect produced in the nerve by stimulus can also be detected by an electrical method. If an isolated piece of nerve be taken and two contacts be made on its surface by means of non-polarisable electrodes at A and B, connection being made with a galvanometer, no current will be observed, as both A and B are in the same physico-chemical condition. The two points, that is to say, are iso-electric. If now the nerve be excited by stimulus, similar disturbances will be evoked at both A and B. If, further, these disturbances, reaching A and B almost simultaneously, cause any electrical change, then, 6 RESPONSE IN TJIE LIVING AND NON-LIVING similar changes taking place at both points, and there being thus no relative difference between the two, the galvanometer will still indicate no current. This nulleffect is due to the balancing action of B as against A. (See fig. 2, a.} Conditions for obtaining electric response — If then we wish to detect the response by means of the galvanometer, one means of doing so will lie in the abolition of this balance, which may be accomplished by making one of the two points, say B, more or less permanently A B A B •< Current of Injury > Current of Action, FIG. 2.— ELECTRIC METHOD OF DETECTING NERVE KESPONSE (a) Iso-electric contacts ; no current in the galvanometer. (b) The anendactBioninjcuurrerdent; cfurrroemntA otfo iBn.jury from B to A : stimulation gives rise to (c) Non-polarisable electrode. irresponsive. In that case, stimulus will cause greater electrical disturbance at the more responsive point, say A, and this will be shown by the galvanometer as a current of response. To make B less responsive we may injure it by means of a cross-sectional cut, a burn, or the action of strong chemical reagents. Current of injury.— We shall revert to the subject of electric response; meanwhile it is necessary to say a few words regarding the electric disturbance caused by the injury itself. Since the physico-chemical conditions of the uninjured A and the injured B are now no longer the same, it follows ELECTRIC RESPONSE 7 that their electric conditions have also become different. They are no longer iso-electric. There is thus a more or less permanent or resting difference of electric potential between them. A current— the current of injury— is found to flow in the nerve, from the injured to the uninjured, and in the galvanometer, through the electrolytic contacts from the uninjured to the injured. As long as there is no further disturbance this current of injury remains approximately con- stant, and is therefore sometimes known as ' the current of rest' (fig. 2,6). A piece of living tissue, unequally injured at the two ends, is thus seen to act like a voltaic element, comparable to a copper and zinc couple. As some confusion has arisen, on the question of whether the injured end is like the zinc or copper in such a combination, it will perhaps be well to enter upon this subject in detail. If we take two rods, of zinc and copper respectively, in metallic contact, and further, if the points A and B are connected bya strip of cloth s moistened with salt solution, it will be seen that we have a complete voltaic element. A current will now flow from B to A in the metal (fig. 3, a) and from A to B through the electrolyte s. Or instead of connecting A and B by a single strip of cloth s, we may connect them by two strips s s', leading to non-polarisable electrodes E E'. The current will then be found just the same as before, i.e. from B to A in the metallic part, and from A through s sf to B, the wire w being interposed, as it were, in the electrolytic part of the circuit. If now a galvanometer be interposed at 0, the current will flow from B to A through the galvanometer, i.e. from right to left. But if we interpose the galvanometer in the electrolytic part of the circuit, that is to say, at w, the same current will appear to flow in the opposite direction. In fig. 3, c, the galvanometer is so interposed, and in this case it is to be noticed that when the current in the galvanometer flows from left to right, the metal connected to the left is zinc. Compare fig. 3, d, where A B is a piece of nerve of which the B end is injured. The current in the galvanometer 8 RESPONSE IN THE LIVING AND NON-LIVING through the non-polarisable electrode is from left to right. The uninjured end is therefore comparable to the zinc in a voltaic cell (is zincoid), the injured being copper-like or cuprIofidt.h1e electrical condition of, say, zinc in the voltaic couple (fig. 3, c) undergo any change (and I shall show later that this can be caused by molecular disturbance), then the exist- ing difference of potential between A and B will also undergo variation. If for example the electrical condition of A approach that of B, the potential difference will undergo a A -B FlG. 3. — DIAGRAM SHOWING THE CORRESPONDENCE BETWEEN INJURED (B) AND UNINJURED (A) CONTACTS IN NERVE, AND Cu AND ZN IN A VOLTAIC ELEMENT Comparison of (c) and (d) will swhiotwh tthhaet Ctuhe ininj(cu)r.ed end of B in (d) corresponds diminution, and the current hitherto flowing in the circuit will, as a consequence, display a diminution, or negative variation. Action current. — We have seen that a current of injury — sometimes known as ' current of rest '— flows in a nerve from the injured to the uninjured, and that the injured B is then less excitable than the uninjured A. If now the nerve be excited, there being a greater 1 In some physiological text-books much wrong inference has been made, based on the supposition that the injured end is zinc-like. ELECTRIC RESPONSE 9 effect produced at A, the existing difference of potential may thus be reduced, with a consequent diminution of the current of injury. During stimula- tion, therefore, a nerve exhibits a negative variation. We may express this in a different way by saying that a ' current of action ' was produced in response to stimulus, and acted in an opposite direction to the current of injury (fig. 2, b). The action current in the nerve is from the relatively more excited to the relatively less excited. Difficulties of present nomenclature. —We shall deal later with a method by which a responsive current of action is obtained without any antecedent current of injury. ' Negative variation ' has then no meaning. Or, again, a current of injury may sometimes undergo a change of direction (see note, p. 12). In view of these considerations it is necessary to have at our disposal other forms of expression by which the direction of the current of response can still be designated. Keeping in touch with the old phraseology, we might then call a current ' negative ' that flowed from the more excited to the less excited. Or, bearing in mind the fact that an uninjured contact acts as the zinc in a voltaic couple, we mSitigmhutlatcailoln itof' ztihnecoiudn,i'njaunrded theend,inajuprperdoxicmonattaicntg *ictuptrooidt.h'e condition of the injured, might then be said to induce a cuproid change. The electric change produced in a normal nerve by stimulation may therefore be expressed by saying that there has been a negative variation, or that there was a current of action from the more excited to the less excited, or that stimulation has produced a cuproid change. The excitation, or molecular disturbance, produced by a stimulus has thus a concomitant electrical expres^ io RESPONSE IN THE LIVING AND NON-LIVING sion. As the excitatory state disappears with the return of the excitable tissue to its original condition, the current of action will gradually disappear.1 The movement of the galvanometer needle during excita- tion of the tissue thus indicates a molecular upset by the stimulus ; and the gradual creeping back of the galvanometer deflection exhibits a molecular recovery. This transitory electrical variation constitutes the t*hreespsotnismeu,l'us.and its intensity varies according to that of Electric recorder. — We have thus a method of obtaining curves of response electrically. After all, it is not essentially very different from the mechanical method. In this case we use a magnetic lever (fig. 4, a), the needle of the galvanometer, which is deflected by the electromagnetic pull of the current, generated under the action of stimulus, just as the mechanical lever was deflected by the mechanical pull of the muscle contracting under stimulus. The accompanying diagram (fig. 4, b) shows how, ' The exciting cause is able to produce a particular molecular rearrangement inthe nerve ; this constitutes the state of excitation and is accompanied by local electrical changes es an ascertained physical concomitant.' ' The excitatory state evoked by stimulus manifests itself in nerve fibres by E.M. changes, and as far as our present knowledge goes by these only. The conception of such an excitable living tissue as nerve implies that of a molecular state which is in stable equilibrium. This equilibrium can be readily upset by an external agency, the stimulus, but the term " stable " expresses the fact that a change in any direction must be succeeded by one of opposite character, this being the return of the living structure to its previous state. Thus the electrical manifestation of the excitatory state is one whose duration depends upon the time during which the external agent is is able to upset and extremely brief, retain in a new then the recoil of poise the the living equilibrium, and if this tissue causes such manifestation to biie. 4it5s3e.lf of very short duration.'— Text-book of Physiology, ed. by Schafer, \ r ELECTRIC RESPONSE under the action of stimulus, the current of rest undergoes a transitory diminution, and how on the cessation of stimulus there is gradual recovery of the tissue, as exhibited in the return of the galvanometer needle to its original position. Two types of response — positive and negative. — It may here be added that though stimu- lus in general pro- (b) duces adiminution of current of rest, or a negative variation (e.g. muscles and nerves), yet, in certain cases, there is an increase, or positive variation. This is seen in the re- sponse ofthe retina to light. Again, a tissue which nor- mally gives a negative variation may A B -< Current of rest >• Current, of action. FIG. 4. — ELECTRIC BECORDER (a) M nomnus-cploelar;iAsinugninejluercedt,rodBes incjounrneedcteinndgs. A EanEd' B with galvanometer G. Stimulus produces c' onnegnaetcitveed vwairtiahtiognal'voafnocmuerrteenrt onfeerdelset. reIcnodredxs curve on travelling paper (in practice, moving galvanometer spot of light traces curve on photographic plate). Rising part of curve rsehcoowvsery.effect of stimulus ; descending part, (b) O is the zero position of the galvanometer; rdienicjmouivrneyirsyh.persodutcheiss daefldeecftlieocntiotno AC B; C; Dstiimsultuhse undergo molecular changes, after which it gives a positive variation. Thus Dr. Waller finds that whereas fresh nerve always gives negative variation, stale nerve sometimes gives positive ; and that retina, which when fresh gives positive, when stale, exhibits negative variation. 12 RESPONSE IN THE LIVING AND NON-LIVING The following is a tabular statement of the two types of response : I. Negative variation. — Action current from more excited to less excited— cuproid change in the excited — e.g. fresh muscle and nerve, stale retina. IE. Positive variation. — Action current from less excited to more excited — zincoid change in the excited — e.Fgr. osmtaltehinserivtew,ilflrebseh retina.1 seen that it is the fact of the electrical response of living substances to stimulus that is of essential importance, the sign plus or minus being a minor consideration. Universal applicability of the electrical mode of response. — This mode of obtaining electrical response is applicable to all living tissues, and in cases like that of muscle, where mechanical response is also available, it is found that the electrical and mechanical records are practically identical. The two response-curves seen in the accompanying diagram (fig. 5), and taken from the same muscle by the two methods simultaneously, clearly exhibit this. Thus we see that electrical response can not only take the place of the mechanical record, but has the further 1 I shall here mention briefly one complication that might arise from regarding the current of injury as the current of reference, and designating the response current either positive or negative in relation to it. If this current of injury remained always invariable in direction — that is to say, from the injured to the uninjured — there would be no source of uncertainty. But it is often found, for example in the retina, that the current of injury undergoes a reversal, or is reversed from the beginning. That is to say, the direction is now from the uninjured to the injured, instead of the opposite. Confusion is thus very apt to arise. No such misunderstanding can however occur if we call the current of response towards the more excited positive, and towards the less excited negative. ELECTRIC RESPONSE advantage of being applicable in cases where the latter cannot be used. Electrical response: A measure of physiological activity.— These electrical changes are regarded as physiological, or characteristic of living tissue, for any conditions which enhance physiological activity also, pari passu, increase their intensity. Again, when the tissue is killed by poison, electrical response disappears, the tissue passing into an irresponsive condition. Anaesthetics, like chloroform, gradually diminish, and finally altogether abolish, electrical response. From these observed facts — that living tissue gives response while a tissue that has been killed does not — it is concluded that the phenomenon of re- sponse ispeculiar to living organisms.1 The response pheno- FmQX ...26 rsi 17 }R{(6).. (9) •.(•4.•).«'3222«.7903'. 17 (10).. Mean response 23-6 B. After 24 hours in chloroform-water C. cuArfiteer ch2l4orhioduers in mer- •25 [Leaves began to j [Leaves began to droop droop in 1 hour and in 4 hours. Deep dis- bent over in 3 hours — aphides dead] vceoilnso.uratiAopnhid•a2el5songd„e•a2t5dh]e | Electric response Electri•c25respo„nse 0 dn. (21^) 11 dn. \ / o •25 „ „ (3) 2 (f4t) 01 (1).... ((32))........ •*2*5* 77„„ ((R76\)) 2l1-5 (m5(.)4..)...... 0 ((68)).... " 7) (9) 1 , \vf* * ' • (10) -5 „ Mean 1 (1(09))........ Mean -15 II. LEAF-STALK OF HORSE-CHESTNUT (1) ....1175 dn„s. (2).... ..10 „ (3).... Mean 14 (1) -5 dn. ((32)) 0 -5 " Mean -3 (1) 000 dn„„ ((32)) Mean 0 ,, These results conclusively prove the physiological nature of the response. I shall in a succeeding chapter give a continuous series of response-curves showing how, owing to progressive death from the action of poison, the responses undergo steady diminution till they are completely abolished. Effect of high temperature. — It is well known that plants are killed when subjected to high temperatures. I took a stalk, and, using the block method, with torsional ELECTRIC RESPONSE IN PLANTS 33 vibration as the stimulus, obtained strong responses at both ends A and B. I then immersed the same stalk for astismhourltatetdimeit ians hboetfowraet.erButat aatbonuetith6e5r° AC.,noarndB caogualidn any response now be evoked. As all the external conditions were the same in the first and second parts of this experiment, the only difference being that in one the stalk was alive and in the other killed, we have here further and conclusive proof of the physiological character of electric response in plants. The same facts may be demonstrated in a still more striking manner by first obtaining two similar but opposite responses in a fresh stalk, at A and B, and then killing one half, say B, by immersing only that half of the stalk in hot water. The stalk is replaced in the apparatus, and it is now found that whereas the A half gives strong response, the end B gives none. In the experiments on negative variation, it was tacitly assumed that the variation is due to a differential action, stimulus producing a greater excitation at the uninjured than at the injured end. The block method enables us to test the correctness of this assumption. The B end of the stalk is injured or killed by a few drops of strong potash, the other end being uninjured. There is a clamp between A and B. The end A is stimulated and a strong response is obtained. The end B is now stimulated, and there is little or no response. The block is now removed and the plant stimulated throughout its length. Though the stimulus now acts on both ends, yet, owing to the irresponsive condition of B, there is a resultant response, which from its direction is found D 34 RESPONSE IN THE LIVING AND NONLIVING to be due to the responsive action of A. This would not have been the case if the end B had been uninjured. We have thus experimentally verified the assumption that in the same tissue an uninjured portion will be thrown into a greater excitatory state than an injured, by the action of the same stimulus. 35 CHAPTER Y PLANT RESPONSE — ON THE EFFECTS OF SINGLE AND OF SUPERPOSED STIMULI STIMULUS Effect of single stimulus — Superposition of stimuli — Additive effect— Staircase effect — Fatigue — No fatigue when sufficient interval between stimuli — Apparent fatigue when stimulation frequency is increased — Fatigue under continuous stimulation. Effect of single stimulus.— In a muscle a single stimulus gives rise to a single twitch which may be re- corded either mechanically or electrically. If there is no fatigue, the successive responses to uniform stimuli are exactly similar. Muscle when strongly stimulated often exhibits fatigue, and successive responses therefore become feebler and feebler. In nerves, however, there is practically no fatigue and successive records are alike. Similarly, in plants, we shall find some exhibiting marked fatigue and others very little. Superposition of stimuli. — If instead of a single stimulus a succession of stimuli be superposed, it happens that a second shock is received before recovery from the first has taken place. Individual effects will then become more or less fused. When the frequency is sufficiently increased, the intermittent effects are fused, and we find an almost unbroken curve. When for example the muscle attains its maximum contraction (corresponding to the frequency and strength of stimuli) it D 2 36 RESPONSE IN THE LIVING AND NON-LIVING is thrown into a state of complete tetanus, in which it appears to be cient for this, held rigid. we have the If the jagged rapidity be not sufficurve of incomplete tetanus. If there is not much fatigue, the upper part FIG. 16. — UNIFORM RESPONSES (RADISH) of the tetanic curve is approximately horizontal, but in cases where fatigue sets in quickly, the fact is shown by the rapid decline of the curve. With regard to all these points we find strict parallels in plant response. In cases where there is no fatigue, the successive responses are identical (fig. 16). With superposition of stimuli we have fusion FIG. 17.— FUSION or EFFECT OF °f effects, analogous tO the RA, PIDLY , SUCCEED. ING STIMUtL etaInus ofPmusclei (/Pfig. ~1i7*)\. (a) m muscle ; (6) m carrot. v to And lastly, the influence of fatigue in plants is to produce a modification of response-curve exactly similar to that of muscle (see bmeenltoiwo)n.ed One effect here. of superposition of stimuli may be PLANT RESPONSE 37 Additive effect. — It is found in animal responses that there is a minimum intensity of stimulus, below which no response can be evoked. But even a sub-minimal stimulus will, though singly ineffective, become effective FIG. 18. — ADDITIVE EFFECT (a) A single stimulus of 3° vibration produced little or no effect, but the same stimulus when rapidly superposed thirty times, produced the large effect (b). (Leaf -stalk of turnip.) by the summation of several. In plants, too, we obtain a similar effect, i.e. the summation of single ineffective stimuli produces effective response (fig. 18). Staircase effect— Animal tissues sometimes exhibit what is known as the ' staircase effect,' that is to say, the heights of successive responses are gradually increased, though the stimuli are maintained constant. This is exhibited typically by cardiac muscle, though it is not unknown even in nerve. The cause is obscure, but it seems to depend on the condition of the tissue. It appears as if the molecular sluggishness of tissue were in these cases only gradually removed under stimulation, and the increased effects were due to increased mole- cular mobility. Whatever be the explanation, I have sometimes observed the same staircase effect in plants (fig. 19). FIG. 19. — ' STAIRCASE EFFECT' IN PLANT Fatigue. — It is assumed that in living substances like muscle, fatigue is caused by the break down or 38 RESPONSE IN THE LIVING AND NON-LIVING dissimilation of tissue by stimulus. And till this waste is repaired by the process of building-up or assimilation, the functional activity of the tissue will remain below par. There may also be an accumulation of the products of dissimilation — 'the fatigue stuffs' — and these latter may act as poisons or chemical depressants. In an animal it is supposed that the nutritive blood supply performs the two-fold task of bringing material for assimilation and removing the fatigue products, thus causing the disappearance of fatigue. This explanation, however, is shown to be insufficient by the fact that an excised bloodless muscle recovers from fatigue after a short period of rest. It is obvious that here the fatigue has been removed by means other than that of renewed assimilation and removal of fatigue products by the circulating blood. It may therefore be instructive to study certain phases of fatigue exhibited under simpler conditions in vegetable tissue, where the constructive processes are in abeyance, and there is no active circulation for the removal of fatigue products. It has been said before that the E.M. variation caused by stimulus is the concomitant of a disturbance of the molecules of the responsive tissues from their normal equilibrium, and that the curve of recovery exhibits the restoration of the tissue to equilibrium. No fatigue when sufficient interval between successive stimuli. — We may thus gather from a study of the response-curve some indication of the molecular distor- tion experienced by the excited tissue. Let us first take the case of an experiment whose record is given PLANT RESPONSE 39 in fig. 20, a. It will be seen from that curve that one minute after the application of stimulus there is a complete recovery of the tissue ; the molecular condition is exactly the same at the end of recovery as in the beginning of stimulation. The second and suc- ceeding response-curves therefore are exactly similar to the first, provided a sufficient interval has been allowed in each case for complete recovery. There is, in such a case, no diminution in intensity of response, that is to say, no fatigue. We have an exactly parallel case in muscles. 6 In muscle with normal circulation and nutrition there is always an inter- val between each pair of (c) St,i.muli,7. i. n W/lliC-/Ll jt//ie FlG-RES2P0O.N—SERECWORHDEN SSHUOFWFIINCGIENT DIMTIINMUETIONis NOOTF hieiq• riit. off> t.wit••ch7d7 oes not, I, n ALLOWED FOR FULL RECOVERY (a) stimuli were applied at intervals of one diminish even a*fter i pro- hmailnfutae;miinnut(e&) ;thtehisinctearuvsaelds awerdeimirneudtuicoend otfo TtrinarCfipefai ePXVMCflntta'tilnO'nn, ann*na/1 response. In (c) the original rhythm is resto£ed,and theVesponseis found to be en- no fatigue appears: l Apparent fatigue when stimulation frequency in- creased.— If the rhythm of stimulation frequency be now changed, and made quicker, certain remarkable modifications will appear in the response-curves. In fig. 20, the first part shows the responses at one minute interval, by which time the individual recovery was complete. The rhythm was now changed to intervals of half 1 Biedermann, Electro-physiology, p, 86. 40 RESPONSE IN THE LIVING AND NON-LIVING a minute, instead of one, while the stimuli were maintained at the same intensity as before. It will be noticed (fig. 20, b) that these responses appear much feebler than the first set, in spite of the equality of stimulus. An inspection of the figure may perhaps throw some light on the subject. It will be seen that when greater frequency of stimulation was introduced, the tissue had not yet had time to effect complete recovery from previous strain. The molecular swing towards equilibrium had not yet abated, when the new stimulus, with its opposing impulse, was received. There is thus a diminution of height in the resultant response. The original rhythm of one minute was now restored, and the succeeding curves (fig. 20, c) at once show increased FIG. 21.C—ELFEARTYIGUE IN response. An analogous instance may Vibration of 30° at inter- be cited in the case of muscle re- vals ofhalf a minute. sponse, where ' the height of twitch diminishes more rapidly in proportion as the excitation interval is shorter.' l From what has just been said it would appear that one of the causes of diminution of response, or fatigue, is the residual strain. This is clearly seen in fig. 21, in a record which I obtained with celerystalk. It will be noticed there that, owing to the imperfect molecular recovery during the time allowed, the succeeding heights of the responses have under- gone a continuous diminution. Fig. 22 gives a 1 Biedermann, loc. tit. PLANT RESPONSE photographic record of fatigue in the leaf-stalk of cauliflower. It is evident that residual strain, other things beingequal, will be greater if the stimuli have been excessive. This is well seen in fig. 23, where the set of first three 4 curves A is for stimulus intensity of 45° vibration, and the second set B, with an augmented response, for stimulus in- tensity of90° vibration. On reverting in c to stimulus intensity of 45°, the responses are seen to have under- gone a great diminution as compared with the first set A. Here is seen Fm. 22. — FATIGUE IN LEAF-STALK OF CAULIFLOWER Stimmauitlnuutsien.t:er3v0a°lsviborfatioonne marked fatigue, the result of overstrain from excessive stimulation. If this fatigue be really due to residual strain effect, then, as strain disappears with time, we may expect the 4-5 4-5 ABC FIG. 23. — EFFECT OF OVERSTRAIN IN PRODUCING FATIGUE Successive stimuli applied at intervals of one minute. The intensity of stimulus in C is the same as that of A, but response is feebler owing to previous over-stimulation. Fatigue is to a great extent removed after fifteen minutes' rest, and the responses in D are stronger than those in C. The vertical line between arrows represents '05 volt. (Turnip leaf-stalk.) responses to regain their former height after a period of rest. In order to verify this, therefore, I renewed the stimulation (at intensity 45°) after fifteen minutes. It 42 RESPONSE IN THE LIVING AND NON-LIVING will at once be seen from record D how far the fatigue had been removed. One peculiarity that will be noticed in these curves is that, owing to the presence of comparatively little residual strain, the first response of each set is rela- tively large. The succeeding responses are approximately equal where the residual strains are similar. The first response of A shows this because it had had long previous rest. The first of B shows it because we are there passing for the first time to increased stimula- tion. The first of c does not show it, because there is now a strong residual strain. D again shows it because the strain has been rreesmt.oved by fifteen minutes' Fatigue under continuous FIG. 24. — KAPID FATIGUE UNDER CON- TINUOUS STIMULATION IN (a) MUSCLE ; (6) IN LEAF-STALK OF CELERY stimulation. — The effect of fatigue is exhibited in marked degree when a tissue is subjected to continuous stimulation. In cases where there is marked fatigue, as for instance in certain muscles, the top of the tetanic curve undergoes rapid decline. A similar effect is obtained also with plants (fig. 24). The effect of rest in producing molecular recovery, and hence in the removal of fatigue, is well illustrated in the following set of photographic records (fig. 25). The first shows the curve obtained with a fresh plant. 43 PLANT RESPONSE The effect is seen to be very large. Two minutes were allowed for recovery, and then stimulation was repeated during another two minutes. The response in this case is seen to be decidedly smaller. A third case is some- what similar to the second. A period of rest of five minutes was now allowed, and the curve obtained FIG. 25. — EFFECT OF CONTINUOUS VIBRATION (THROUGH 50°) IN CARROT In trheecofviresrty.threTeherelcaosrtdsr,ectowrod mwiansutetsa'kenstiafmtuelrattihoen sipsefcoilmleowned habdy atwroestminouftefsiv'e minutes. The response, owing to removal of fatigue by rest, is stronger. subsequently, owing to partial removal of residual strain, is found to exhibit greater response. The results thus arrived at, under the simple conditions of vegetable life, free as they are from all possible complications and uncertainties, may perhaps throw some light on the obscure phenomena of fatigue in animal tissues. 44 RESPONSE IN THE LIVING AND NON-LIVING CHAPTEE VI PLANT RESPONSE — ON DIPHASIC VARIATION Diphasic variation — Positive after-effect and positive response — Radial E.M. variation. WHEN a plant is stimulated at any point, a molecular disturbance — the excitatory wave — is propagated outwards from the point of its initiation. Diphasic variation. — This wave of molecular disturbance isattended by a wave of electrical disturbance. (Usually speaking, the electrical relation between disturbed and less disturbed is that of copper to zinc.) It takes some time for a disturbance to travel from one point to another, and its intensity may undergo a diminution as it recedes further from its point of origin. Suppose a disturbance originated at C ; if two points are taken near each other, as A and B, the disturbance will reach them almost at the same time, and with the same intensity. The electric disturbance will be the same in both. The effect produced at A and B will balance each other and there will be no resultant current. By killing or otherwise reducing the sensibility of B as is done in the method of injury, there is no response at B, and we obtain the unbalanced response, due to disturbance at A ; the same effect is obtained by putting PLANT RESPONSE 45 a clamp between A and B, so that the disturbance may not reach B. But we may get response even without injury or block. If we have the contacts at A and B, and if we give a tap nearer A than B (fig. 26, a), then we have (1) the disturbance reaching A earlier than B. (2) The disturbance reaching A is much stronger than at B. The disturbance at B may be so comparatively feeble as to be negligible. It will thus be seen that we might obtain responses even without injury or block, in cases where the disturbance is enfeebled in reaching a distant point. In such a case on giving a tap near A a responsive current would be produced in one direction, and in the opposite direction when the tap is given near B (fig. 26, b). Theoretically, then, we might find a neutral point between A and B, so that, on originating the disturbance there, the waves of disturbance would reach A and B at the same instant and with the same intensity. If, further, the rate of recovery be the same for both points, then the electric disturbances produced at A and B will continue to balance each other, and the galvanometer will show no current. On taking a cylindrical root of radish I have sometimes succeeded in finding a neutral point, which, being disturbed, did not give rise to any resultant current. But disturbing a point to the right or to the left gave rise to opposite currents. It is, however, difficult to obtain an absolutely cylindrical specimen, as it always tapers in one direction. The conductivity towards the tip of the root is not exactly the same as that in the ascending direction. It 46 RESPONSE IN THE LIVING AND NON-LIVING is therefore difficult to fix an absolutely neutral point, but a point may be found which approaches this very nearly, and on stimulating the stalk near this, a very interesting diphasic variation has been observed. In a specimen of cauliflower-stalk, (1) stimulus was applied very much nearer A than B (the feeble disturbance reaching B was negligible). The resulting response was upward and the recovery took place in about sixty seconds. FIG. 26. — DIAPHASIC VARIATION (2) Stimulus was next applied near B. The resulting response was now downward (fig. 26, b). (3) The stimulus was now applied near the approximately neutral point N. In this case, owing to a slight difference in the rates of propagation in the two directions, a very interesting diphasic variation was produced (fig. 26, c). From the record it will be seen that the disturbance arrived earlier at A than at B. This produced an upward response. But during the PLANT RESPONSE 47 subsidence of the disturbance at A, the wave reached B. The effect of this was to , produce a current in the opposite direction. This apparently hastened the recovery of A (from 60 seconds to 12 seconds). The excitation of A now disappeared, and the second phase of response, that due to excitation of B, was fully displayed. Positive after-effect.— If we regard the response due to excitation of A as negative, the later effect on B would appear as a subsequent positive variation. In the response of nerve, for example, where contacts are made at two surfaces, injured and uninjured, there is sometimes observed, first a negative variation, and then a positive after-effect. This may sometimes at least be due to the proximal uninjured contact first giving the usual negative variation, and the more distant contact of injury giving rise, later, to the opposite, that is to say, apparently positive, response. There is always a chance of an after-effect due to this cause, unless (1) the injured end be completely killed and rendered quite irresponsive, or (2) there be an effective block between A and B, so that the disturbance due to stimulus can only act on one, and not on the other. I have found cases where, even when there was a perfect block, a positive after-effect occurred. It would thus appear that if molecular distortion from stimulus give rise to a negative variation, then during the process of molecular recovery there may be overshooting of the equilibrium position, which may be exhibited as a positive variation. 48 RESPONSE IN THE LIVING AND NON-LIVING Positive variation. — The responses given by muscle or nerve are, normally speaking, negative. But that of retina is positive. The sign of response, however, is apt to be reversed if there be any molecular modification of the tissue from changes of external circumstances. Thus it is often found that nerve in a stale condition gives positive, instead of the normal negative variation, and stale retina often gives negative, instead of the usual positive. Curiously enough, I have on many occasions found exactly parallel instances in the response of plants. FIG. 27. — ABNORMAL POSITIVE KESPONSES IN STALE LEAF-STALK OF TURNIP CONVERTED INTO NORMAL NEGATIVE UNDER STRONG STIMULATION1 The relative intensities of stimuli in the two cases are in the ratio of 1 : 7. Plants when fresh, as stated, give negative responses as a rule. But when somewhat faded they sometimes give rise to positive response. Again, just as in the modified nerve the abnormal positive response gives place to the normal negative under strong and longcontinued stimulation, so also in the modified plant the abnormal positive response passes into negative 1 For general purposes it is immaterial whether the responses are recorded up or down. For convenience of inspection they are in general recorded up. But in cases where it is necessary to discriminate the sign of response, positive response will be recorded up, and negative down. PLANT RESPONSE 49 (fig. 27) under strong stimulation. I was able in some cases to trace this process of gradual reversal, by continuously increasing the intensity of stimulus. It was then found that as the stimulus was increased, the positive at a certain point underwent a reversal into the normal negative response (fig. 28). The plant thus gives a reversed response under abnormal conditions of staleness. I have sometimes FIG. 28.— ABNORMAL POSITIVE PASSING INTO NORMAL NEGATIVE IN A STALE SPECIMEN OF LEAF-STALK OF CAULIFLOWER Stimulus was gradually increased from 1 to 10, by means of spring-tapper. When the stimulus intensity was 10, the response became reversed into normal negative. (Parts of 8 and 9 are out of the plate.) found similar reversal of response when the plant is subjected to the abnormal conditions of excessively high or low temperature. Radial E.M. variation. — We have seen that a current of response flows in the plant from the relatively more to the relatively less excited. A theoretically important experiment is the following: A thick stem of plant stalk was taken and a hole bored so as to make one contact with the interior of the tissue, the other being E 5o RESPONSE IN THE LIVING AND NON-LIVING on the surface. After a while the current of injury was found to disappear. On exciting the stem by taps or torsional vibration, a responsive current was observed which flowed inwards from the more disturbed outer surface to the shielded core inside (fig. 29). Hence it is seen that when a wave of disturbance is propagated FIG. 29.-EADIAL E.M. VARIATION caloonncgomitthaentPlawnatv>e tnoefre rad^iala E.M. variation. The swaying of a tree by the wind would thus appear to give rise to a radial E.M.F. CHAPTEB VII PLANT RESPONSE — ON THE RELATION AND RESPONSE BETWEEN STIMULUS Increased response with increasing stimulus — Apparent diminution of response with excessively strong stimulus. As already said, in the living tissue, molecular disturbance induced by stimulus is accompanied by an electric disturbance, which gradually disappears with the return of the disturbed molecules to their position of equilibrium. The greater the molecular distortion produced by the stimulus, the greater is the electric variation produced. The electric response is thus an outward expression of a molecular disturbance produced by an external agency, the stimulus. Curve of relation between stimulus and response.— In the curve showing the relation between stimulus and response in nerve and muscle, it is found that the molecular effect as exhibited either by contraction or E.M. variation in muscle, or simply by E.M. variation in nerve, is at first slight. In the second part, there is a rapidly increasing effect with increased stimulus. Finally, a tendency shows itself to approach a limit of response. Thus we find the curve at first slightly convex, then straight and ascending, and lastly, concave to the abscissa (fig. 30). In muscle the limit of response is reached much sooner than in nerve. As will be seen, the range of variation of stimulus in these curves is not very BS 52 RESPONSE IN THE LIVING AND NON-<-Ltr IVING threat. When the stimulus is carried beyond moderate limits, the response, owing to fatigue or other causes, may sometimes undergo an actual diminution. e,_ ei Nen /x '. .M 7Rfee spt imrse / ^ t-~- •.— cle «* Li fL t j 1 |2 1-2 !•* 1-6 1-6 2-0 2-2 2-* 2-6 2-8 3-0 3-2 3-* 3'6 3-6 4.-0 ,' .-' / ' d- FIG. 30. — CURVES SHOWISNTGIMUTLHUES KAENLDATIEOENSPOBNESTEWEEN THE INTENSITY OF Abscissae indicate increasing intudteeofnrseisptoynsoef. stim(uWlausl.ler.)Ordinates indicate magni- I have obtained very interesting results, with reference to the relation between stimulus and response, when experimenting with plants. These results are suggestive of various types of response met with in animal tissues. 1. In order to obtain the simplest type of effects, not com- Fm 31 plicated by secondary phenomena, Taps1:2:of3:4increaspirnogducisntgrengti h n- OU6 liaS tO choOS6 . . Specimens which Ceased response in leaf- exhl bit little cured these, iatlgU6. Having I undertook two seprriOe-s of experiments. In the first (A) the stimulus was applied by means torsional of the spring-tapper, vibration. and in the second (£) by PLANT RESPONSE 53 (A) The first stimulus was given by a fall of the lever through A, the second through 2 /i, and so on. The response-curves clearly show increasing effect with increased stimulus (fig. 31). 5° 7J° 10° 12J° FIG. 32. — INCREASED KESPONSE WITH INCREASING VIBRATIONAL STIMULI (CAULIFLOWER-STALK) Stimuli applied at intervals of three minutes. Vertical line^'l volt. (B) 1. The vibrational stimulus was increased from 2-5° to 5° to 7*5° to 10° to 12'5° in amplitude. It will be observed how the intensity of response tends to approach a limit (fig. 32). TABLE SHOWING THE INCREASED E.M. VARIATION PRODUCED BY INCREASING STIMULUS Angle of Vibration 2-5° E.M.F. ••004754 vol„t •090 „ •100 „ •106 „ 7-5° 12-5°10° 5° 54 RESPONSE IN THE LIVING AND NON-LIVING 2. The next figure shows-how little variation is produced with low value of stimulus, but with increasing stimulus the response undergoes a rapid increase, after which it tends to approach a limit (fig. 33, a). 3. ,\s an extreme instance of the case just cited, I have often come across a curious phenomenon. During the gradual increase of the stimulus from a low value there would be apparently no response. But Ib) A— A 12 16 22 32 4-5 10° 20° FIG. 33. — RESPONSES TO INCREASING STIMULI PRODUCED ANGLE OF VIBRATION 4-0 30C BY INCREASING .(a) Record with a specimen of fresh radish. Stimuli applied at intervals of two minutes. The record is taken for one minute. ' (6) Record for stale radish. There is a reversed response for the feeble stimulus of 5° vibration. when a critical value was reached a maximum response would suddenly occur, and would not be exceeded when the stimulus was further increased. Here we have a parallel to what is known in animal physiology as the ' all or none ' principle. With the cardiac muscle, for example, there is a certain minimal intensity which is effective in producing response, but further increase of stimulus produces no increase in response. 4. From an inspection of the records of responses PLANT RESPONSE 55 which are given, it will be seen that the slope of a curve which shows the relation of stimulus to response will at first be slight, the curve will then ascend rapidly, and at high values of stimulus tend to become horizontal. The curve as a whole becomes, first slightly convex to the abscissa, then straight and ascending, and lastly concave. A far more pronounced convexity in the first part is shown in some cases, especially when the specimen is stale. This is due to the fact that under these circumstances response is apt to begin with an actual reversal of sign, the plant under feebler than a certain critical intensity of stimulus giving positive, instead of the normal negative* response (fig. 33, b). Diminution of response with excessively strong stimulus. — It is found that in animal tissues there is sometimes an actual diminution of response with excessive increase of stimulus. Thus Waller finds, in working with retina, that as the intensity of light stimulus is gradually increased, the response at first increases, and then sometimes undergoes a diminution. This phenomenon is unfortunately complicated by fatigue, itself regarded as obscure. It is therefore difficult to say whether the diminution of response is due to fatigue or to some reversing action of an excessively strong stimulus. From fig. 33, b, above, it is seen that there was an actual reversal of response in the lower portion of the curve. It is therefore not improbable that there may be more than one point of reversal. In physical phenomena we are, however, acquainted with numerous instances of reversals. For example, 56 RESPONSE IN THE LIVING AND NON-LIVING a common effect of magnetisation is to produce an elongation of an iron rod. But Bidwell finds that as the magnetising force is pushed to an extreme, at a certain point elongation ceases and is succeeded, with further increase of magnetising force, by an actual contraction. Again a photographic plate, when exposed continuously to light, gives at first a negative image. Still longer exposure produces a positive. Then again we have a negative. There is thus produced a series of recurrent reversals. In photographic prints of flashes of lightning, two kinds of images are observed, one, the positive — when the lightning discharge is moderately intense — and the other, negative, the so-called ' dark lightning '— due to the reversal action of an intensely strong discharge. In studying the changes of conductivity produced in metallic particles by the stimulus of Hertzian, radiation, I have often noticed that whereas feeble radiation pro- duces one effect, strong radiation produces the opposite. Again, under the continuous action of electric radiation, I have frequently found recurrent reversals.1 Diminution of response under strong stimulus traced to fatigue. — But there are instances in plant response where the diminution effect can be definitely traced to fatigue. The records of these cases are extremely suggestive as to the manner in which the diminu- tion is brought about. The accompanying figures (fig. 34) give records of responses to increasing stimulus. They were made with specimens of cauliflower-stalks, one of which (a) showed little fatigue, while in the other (b) 1 See ' On Electric Touch,' Proc. Roy. Soc. Aug. 1900. PLANT RESPONSE fatigue was present. It will be seen that the curve5s7 obtained by joining the apices of the successive single responses are very similar. In one case there is no fatigue, the recovery from each stimulus being complete. Every response in the 30 20 30° 35 FIG. 34. — KESPONSES TO INCREASING STIMULUS OBTAINED WITH Two SPECIMENS OF STALK OF CAULIFLOWER In (a) fatigue is absent, in (6) it is present. series therefore starts from a position of perfect equilibrium, and the height of the single responses increases with increasing stimulation. But in the second case, 58 RESPONSE IN THE LIVING AND NON-LIVING the strain is not completely removed after any single stimulation of the series. That recovery is partial is seen by the gradual shifting of the base line upwards. In the former case the base line is horizontal and re- presentsacondition of complete equilibrium. Now, however, the base line, or line of modified equilibrium, is tilted upwards. Thus even in this case if we measure the heights of successive responses from the line of absolute equilibrium, they will be found to increase with increasing stimulus. Ordinarily, however, we make no allowance for the shifting of the base line, measuring response rather from the place of its previous recovery, or from the point of modified equilibrium. Judged in this way, the responses undergo an apparent diminution. 59 CHAPTEE VIII PLANT RESPONSE — ON THE INFLUENCE OF TEMPEEATURE Effect of very low temperature — Influence of high temperature— Determination ofdeath-point — Increased response as after-effect of temperature variation — Death of plant and abolition of response by the action of steam. FOR every plant there is a range of temperature most favourable to its vital activity. Above this optimum, the vital activity diminishes, till a maximum is reached, when it ceases altogether, and if this point be maintained for a long time the plant is apt to be killed. Similarly, the vital activity is diminished if the temperature be lowered below the optimum, and again, at a minimum point it ceases, while below this minimum the plant may be killed. We may regard these maximum and minimum temperatures as the death- points. Some plants can resist these extremes better than others. Length of exposure, it should however be remembered, is also a determining factor in the question as to whether or not the plant shall survive unfavourable conditions of tem- perature Thus we have hardy plants, and plants that are affected by excessive variations of temperature. Within the characteristic power of the species, there may be, again, a certain amount of individual difference. These facts being known, I was anxious to deter- 60 RESPONSE IN THE LIVING AND NON-LIVING mine whether the undoubted changes induced by temperature inthe vital activity of plants would affect electrical response. Effect of very low temperature.— As regards the influence of very low temperature, 1 had opportunities of studying ths question on the sudden appearance of frost. In the previous week, when the tempera- ture was about 10° C., I had obtained strong electric response in radishes whose value varied from *05 to •1 volt. But two or three days later, as the effect of the frost, I found electric response to have practically disappeared. A few radishes were, however, found somewhat resistant, but the electric response had, even in these cases, fallen from the average value of "075 Y. under normal temperature to *003 V. after the frost. That is to say, the average sensitiveness had been reduced to about -^V11. On warming the frost-bitten radish to 20° C. there was an appreciable revival, as shown by increase in response. In specimens where the effect of frost had been very great, i.e. in those which showed little or no electric response, warming did not restore responsiveness. From this it would appear that frost killed some, which could not be subsequently revived, whereas others were only reduced to a condition of torpidity, from which there was revival on warming. I now tried the effect of artificial lowering of temperature on various plants. A plant which is very easily affected by cold is a certain species of Eucharis lily. I first obtained responses with the leaf-stalk of this lily at the ordinary temperature of the room PLANT RESPONSE 61 (17° C.). I then placed it for fifteen minutes in a cooling chamber, temperature — 2° C., for only ten minutes, after which, on trying to obtain response, it was found to have practically disappeared. I now warmed the plant by immersing it for awhile in water at 20° C., and this produced a revival of the response (fig. 35). If the plant be subjected tolow temperature for too long a time, there is then no subsequent revival. I obtained a similar marked diminution of response with the flower-stalk of Arum lily, on lowering the temperature to zero. My next attempt was to compare the sensibility of different plants to the effect of lowered temperatures. For this purpose I chose three specimens : (1) Eucharis lily ; (2) FIG. 35. — DIMINUTION OF KESPONSE IN EUCHAKIS BY LOWERING OF TEMPERATURE (a) Normal response at 17° C. (b) The response almost disappears when plantfis subjected to -2° C. for fifteen minutes. (r) Kevival of response 011 warming to 20° C. Ivy ; and (3) Holly. I took their normal response at 17° C., and found that, generally speaking, they attained a fairly constant value after the third or fourth response. After taking these records of normal response, I placed the specimens in an ice-chamber, 62 RESPONSE IN THE LIVING AND NON-LIVING temperature 0°C., for twenty-four hours, and afterwards took their records once more at the ordinary tempera- ture of the room. From these it will be seen that while the responsiveness of Eucharis lily, known to be susceptible to the effect of cold, had entirely disappeared, that of the hardier plants, Holly and Ivy, showed very little change (fig. 36). Another very curious effect that I have noticed is that when a plant approaches its death-point by reason of excessively high or low temperature, not only is its general responsiveness diminished almost to zero, but even the slight response occasionally becomes reversed. Ivy Holly Eucharis FIG. 36. — AFTER-EFFECT OF COLD ON IVY, HOLLY, .AND EUCHARIS LILY a. The normal response ; 6. Eesponse after subjection to freezing temperature for twenty-four hours. Influence of high temperature, and determination of death-point. — I next tried to find out whether a rise of temperature produced a depression of response, and whether the response disappeared at a maximum tem- perature— the temperature of death-point. For this purpose I took a batch of six radishes and obtained from them responses at gradually increasing temperatures. These specimens were obtained late in the season, and their electric responsiveness was much lower than those obtained earlier. The plant, previously kept for five minutes in water at a definite temperature PLANT RESPONSE (say 17° C.), was mounted in the vibration apparatus arid responses observed. The plant was then dismounted, and replaced in the water-bath at a higher temperature (say 30° C.) again, for five minutes. A second set of responses was now taken. In this way observations were made with each specimen till the temperature at which response almost or altogether ceased was reached. I give below a table of results obtained with six specimens of radish, from which it would appear that response begins to be abolished in these cases at temperatuvr.)es varying from 53° to TABLE SHOWING 55° C. EFFECT OF HIGH TEMP'EK'ATTJKE ABOLISHING RESPONSE IN o „ Temperaturere Galvanometric response Temperature Galvanometric response o „ 3 (100 dn7s0. d=ns'.07 V.) (17° <5 (53° , * V 160I „ \ 100 „ W 15i05°3°j!,7° 2 „ Electricj!7h°eating. — The (4) C JJ (1..0.0 d84n00s. d=ns„-.07 JJ . ,. 600 „„ • )) (6) » 160°{5?J5° experiments (17j°ust described were, however, rather troublesome, inasmuch as, in order to produce each variation of temperature, the specimen had to be taken out of the apparatus, warmed, and remounted. I therefore introduced a modification by which this difficulty was obviated. The specimen was now enclosed in a glass chamber (fig. 37), which also contained a spiral of German-silver wire, through which electric currents could be sent, for the purpose of heating the chamber. By varying the intensity of the current, the temperature could be regulated at will. The specimen chosen for experiment was the leaf-stalk of celery. It was kept at each given temperature for 64 RESPONSE IN THE LIVING AND NON-LIVING ten minutes, and two records were taken during that time. It was then raised by 10° C., and the same process FIG. 37. — THE GLASS CHAMBER CONTAINING THE PLANT Amplitude of vibration which determines the intensity of stimulus is measured by the graduated circle seen to the right. Temperature is regulated by the electric heating coil K. For experiments on action of anaesthetics, vapour of chloroform is blown in through the side tube. was repeated. It will be noticed from the record (fig. 38) that in this particular case, as the temperature 20°C V 1 min. FIG. 38. — EFFECT OF TEMPERATURE ON KESPONSE The response was abolished at the hot-water temperature of 55° C. rose from 20° C. to 30° C., there was a marked diminution of response. At the same time, in this case at PLANT RESPONSE 65 least, recovery was the response was 21 quicker. At 20° C., for dns., and the recovery was example, not com- plete in the course of a minute. At 30° C., however, the response had been reduced to 7'5 divisions, but there was almost complete recovery in twelve seconds. As the temperature was gradually increased, a con- tinuous decrease of response occurred. This diminution of response with increased temperature appears to be universal, but the quickening of recovery may be true of individual cases only. TABLE SHOWING DIMINUTTIEOMNPEROPATURERSEPONSE WITH INCREASING Temper2at0u°re 30° 40° (•01 Volt = 35 divisions) R21esponse 7-5 5-5 Temper5at0u°re Resp4onse In radishes response disappeared completely at 55° C , but with celery, heated in the manner described, I could not obtain its entire abolition at 60° C. or even higher. A noticeable circumstance, howeve6r5°, was the prolongation of the period of recovery at these high temperatures. I soon understood the reason of this apparent anomaly. The method adopted in the present case was that of dry heating, whereas the previous experiments had been carried on by the use of hot water. It is well known that one can stand a temperature of 100° C. without ill effects in the hot-air chamber of a Tbeurkfaitsahl. bath, while immersion in water at 100° C. would In order to find out whether subjection to hot water would kill the celery-stalk, I took it out and placed it F 66 RESPONSE IN THE LIVING AND NON-LIVING for five minutes from the record in water at 55° C. taken afterwards, This, as will be seen effectively killed the plant (fig: 38, w). Increased sensitiveness as after-effect of temperature variation.— A very curious effect of temperature variation isthe marked increase of sensitiveness which often 19* C 30 C 50 C 25°C faUiruj Temperature, 50 C 70 C Temperature rising >- FIG. 39. — EFFECT OF RISING AND FALLING TEMPERATURE ON THE RESPONSE OF SCOTCH KALE appears as its after-effect. I noticed this first in a series of observations where records were taken during the rise of temperature and continued while the tempera- ture was falling (fig. 39). The temperature was adjusted by electric heating. It was found that the responses were markedly enhanced during cooling, as PLANT RESPONSE compared with responses given at the same temperatures while warming (see table). Temperature variation thus seems to have a stimulating effect on response, by increasing molecular mobility in some way. The second FIG. 40.— KECORDS OF KESPONSES IN EUCHARIS LILY DURING KISE AND FALL OF TEMPERATURE Stimulus constant, applied at intervals of one minute. The temperature of plant-chamber gradually rose on starting current in the heating coil ; on breaking current, the temperature fell gradually. Temperature corresponding to each record is given below. Temperature rising: (1) 20°, (2) 20°, (3) 22°, (4) 38°, (5) 53°, (6) 68°, (7) 65°. Temperature falling : (8) 60°, (9) 51°, (10) 45°, (11) 40°, (12) 38°. record (fig. 40) shows the variation of response in Eucharis lily (1) during the rise, and (2) during the fall TABLE SHOWING THE VARIATION OF RESPONSE IN SCOTCH KALE DURING THE RlSE AND FALL OF TEMPERATURE Temperature Kesponse . Eesponse [Temperature rising] [Temperature falling] 19° C. 25° „ 30° „ 5700°° „„ ...... ... ... . . . . 47 dns. . . 2114 ....... 8 ....... 7 28 dns. 16 ,. — F 2 68 RESPONSE IN THE LIVING AND NON-LIVING of temperature. Fig. 41 gives a curve of variation of response during the rise and fall of temperature. Point of temperature maximum. — We have seen how, in cases of lowered temperature, response is abolished earlier in plants like Eucharis, which are affected by cold, than in the hardier plants such as Holly and Ivy. Plants again are unequally affected as regards the upper range. In the case of Scotch kale, for instance, response disappears after ten minutes of water temperature of about 55° C., but with Eucharis fairly marked response can still be obtained after such 20C 60°C. FIG. 41. — CURVE SHOWING VAKIATION OF RESPONSE IN EUCHARIS WITH THE RISE AND FALL OF TEMPERATURE immersion and does not disappear till it has been subjected for ten minutes to hot water, at a temperature of 65° C. or even higher. The reason of this great power of resistance to heat is probably found in the fact that the Eucharis is a tropical plant, and is grown, in this country, in hot-houses where a comparatively high temperature is maintained. The effect of steam. — I next wished to obtain a continuous record by which the effects of suddenly increased temperatures, culminating in the death of the plant, might be made evident. For this purpose I mounted the plant in the glass chamber, into which steam PLANT RESPONSE eould be introduced. I had chosen a specimen which gave regular response. On the introduction of steam, with the consequent sudden increase of temperature, there was a transitory augmentation of excitability. But this quickly disappeared, and in five minutes the plant was effectively killed, as will be seen graphically illustrated in the record (fig. 42). Before f After FIG. 42.— EFFECT OF STEAM IN KILLING RESPONSE The two records to the left exhibit normal response at 17" C. Sudden warming by stseurae tmo stpearmodukcieldled atthfeirsptlaannt i(nccarreroats)e aonfdreasbpoolnisseh,edbutthefirveespmoinnsuet.es' expo- Vibrlainteio=na'll vosltt.imulus of 30° applied at intervals of one minute; vertical It will thus be seen that those modifications of vital activity which are produced in plants by temperature variation can be very accurately gauged by electric response. Indeed it may be said that there is no other method by which the moment of cessation of vitality can be so satisfactorily distinguished. Ordinarily, we 70 RESPONSE IN THE LIVING AND NON-LIVING are able to judge that a plant has died, only aftervarious indirect effects of death, such as withering, have begun to appear. But in the electric response we have an immediate indication of the arrest of vitality, and we are thereby enabled to determine the death-point, which it is impossible to do by any other means. It may be mentioned here that the explanation suggested by Kunkel, of the response being due to movement of water in the plant, is inadequate. For in that case we should expect a definite stimulation to be under all conditions followed by a definite elec- tric response, whose intensity and sign should remain invariable. But we find, instead, the response to be profoundly modified by any influence which affects the vitality of the plant. For instance, the response is at its maximum at an optimum temperature, a rise of a few degrees producing a profound depression ; the response disappears at the maximum and minimum temperatures, and is revived when brought back to the optimum. Anaesthetics and poisons abolish the response. Again, we have the response undergoing an actual reversal when the tissue is stale. All these facts show that mere movement of water could not be the effective cause of plant response. CHAPTEE IX PLANT KESPONSE — EFFECT OF ANAESTHETICS AND POISONS Effect of anaesthetics, a test of vital character of response — Effect of chloroform— Effect of chloral — Effect of formalin — Method in which response isunaffected by variation of resistance — Advantage of block method — Effect of dose. THE most important test by which vital phenomena are distinguished is the influence on response of narcotics and poisons. For example, a nerve when narcotised by chloroform exhibits a diminishing response as the action of the anaesthetic proceeds. (See below, fig. 43.) Similarly, various poisons have the effect of permanently abolishing all response. Thus a nerve is killed by strong alkalis and strong acids. I have already shown how plants which previously gave strong response did not, after application of an anaesthetic or poison, give any response at all. In these cases it was the last stage only that could be observed. But it appeared important to be able to trace the growing effect of anassthetisation or poisoning throughout the process. There were, however, two conditions which it at first appeared difficult to meet. First it was necessary to find a specimen which would normally exhibit no fatigue, and give rise for a long time to a uniform series 72 RESPONSE IN THE LIVING AND NON-LIVING of response. The immediate changes made in the response, in consequence of the application of chemical reagents, could then be demonstrated in a striking manner. And with a little trouble, specimens can be secured in which perfect regularity of response is found. The record given in fig. 16, obtained with a specimen of radish, shows how possible it is to secure plants in which response is absolutely regular. I subjected this to uniform stimulation at intervals of one minute, dur- ing half an hour, without detecting the least variation Before ^ After FIG. 43. — EFFECT OF CHLOROFORM ON NERVE KESPONSE (WALLER) in the responses. But it is of course easier to find others in which the responses as a whole may be taken as regular, though there may be slight rhythmic fluctuations. And even in these cases the effect of reagents is too marked and sudden to escape notice. For the obtaining of constant and strong response I found the best materials to be carrot and radish, selected individuals from which gave most satisfactory results. The carrots were at their best in August and September, PLANT RESPONSE 73 after which their sensitiveness rapidly declined. Later, being obliged to seek for other specimens, I came upon radish, which gave good results in the early part of November ; but the setting-in of the frost had a prejudicial effect on its responsiveness. Less perfect than these, but still serviceable, are the leaf-stalks of turnip and cauliflower. In these the successive responses as a whole may be regarded as regular, though a curious alternation is sometimes noticed, which, however, has a regularity of its own. My second misgiving was as to whether the action of reagents would be sufficiently rapid to display itself within the time limit of a photographic record. This would of course depend in turn upon the rapidity with which the tissues of the plant could absorb the reagent and be affected by it. It was a surprise to me to find that, with good specimens, the effect was manifested in the course of so short a time as a minute or so. Effect of chloroform. — In studying the effect of chemical reagents in plants, the method is precisely similar to that employed with nerve ; that is to say, where vapour of chloroform is used, it is blown into the plant chamber. In cases of liquid reagents, they are applied on the points of contact A and B and their close neighbourhood. The mode of experiment was (1) to obtain a series of normal responses to uniform stimuli, applied at regular intervals of time, say one minute, the record being taken the while on a photographic plate. (2) Without interrupting this procedure, the anassthetic agent, vapour of chloroform, was blown into the closed chamber containing the plant. 74 RESPONSE IN THE LIVING AND NON-LIVING It will be seen how rapidly chloroform produces depression of response (fig. 44), and how the effect grows with time. In these experiments with plants, the same curious shifting of the zero line is sometimes noticed as in nerve when subjected similarly to the action of re- agents. This is a point of minor importance, the * Before f After FIG. 44. —EFFECT OF CHLOROFOEM ON RESPONSES OF CARROT Stimuli of 25° vibration at intervals of one minute. essential point to be noticed being that the responses are rapidly reduced. Effects of chloral and formalin.— I give below (figs. 45, 46) two sets of records, one for the reagent chloral and the other for formalin. The reagents were applied in the form of a solution on the tissue at the two leading contacts, and the contiguous surface. The rhythmic fluctuation in the normal response shown in fig. 45 is interesting. The abrupt decline, within a 75 PLANT RESPONSE minute of the application of chloral, is also extremely well marked. U.U.- Before After FIG. 45.— ACTION OF CHLORAL HYDRATE ON THE RESPONSES OF LEAF-STALK OF CAULIFLOWER Vibration of 25° at intervals of one minute. Response unaffected by variation of resistance. — In order to bring out clearly the main phenomena, I have postponed till now the consideration of a point of some Before ^ After FIG. 46. — ACTION OF FORMALIN (RADISH) difficulty. To determine the influence of a reagent in modifying the excitability of the tissue, we rely upon its effect in exalting or depressing the responsive E.M. 7 6 RESPONSE IN THE LINING AND NON-LIVING variation. We read this effect by means of galvanometric deflections. And if the resistance of the circuit remained constant, then an increase of galvanometer deflection would accurately indicate a heightened or depressed E.M. response, due 'to greater or less excitability of tissue caused by the reagent. But, by the introduction of the chemical reagent, the resistance of the tissue may undergo change, and owing to this cause, modification of response as read by the galvano- meter may be produced without any E.M. variation. The observed variation of response may thus be partly owing to some unknown change of resistance, as well as to that of the E.M. variation in response to stimulus. We may however discriminate as to how much of the observed change is due to variation of resistance by comparing the deflections produced in the galvanometer by the action of a definite small E.M.F. before and after the introduction of the reagent. If the deflections be the same in both cases, we know that the resistance has not varied. If there have been any change, the variation of deflection will show the amount, and we can make allowance accordingly. I have however adopted another method, by which all necessity of correction is obviated, and the galvanometric deflections simply give E.M. variations, unaffected by any change in the resistance of the tissue. This is done by interposing a very large and constant resistance in the external circuit and thereby making other resistances negligible. An example will make this point clear. Taking a carrot as the vegetable tissue, I found its resistance plus the resistance of the non-